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Last updated date: 28th Nov 2023
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MVSAT Dec 2023

In an Amplitude Modulation
a) Amplitude of the carrier varies
b) Frequency of the carrier remains constant
c) Phase of the carrier remains constant
d) all of the above

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Hint: The amplitude of the carrier signal alters by the instantaneous amplitude of the modulating signal. This means the amplitude of the carrier signal carrying no information alters as per the signal's amplitude containing the message at each moment. In Amplitude Modulation, the carrier waves amplitude changes, and message signals are changed over them. The frequency of the carrier persists constant, and the phase of carrier waves also persists constant.

Complete step-by-step solution:
A continuous wave moves on continuously without any time periods, and it is the baseband information signal, which contains the data. This wave has to be changed. Amplitude modulation is a modulation method used in electronic transmission, most commonly for conveying messages with a radio carrier wave. In amplitude modulation, the amplitude of the carrier wave is changed in proportion to the message signal, such as an audio sign. This technique varies with angle modulation, in which either the carrier wave's frequency is varied as in frequency modulation, or its phase varies, as in phase modulation.
AM was the quickest modulation method utilized for transmitting audio in radio broadcasting. Phase and frequency of the carrier wave is constant. In electronics, modulation means changing some features of a continuous wave signal with message-bearing modulation waveforms, such as an audio signal expressing a sound or a video signal signifying image. The carrier wave has a much greater frequency than the information signal, which carries the information. At the making station, the message signal is derived from the modulated transmitter by demodulation.
In amplitude modulation, the amplitude of the carrier oscillations is changed. For example, in AM radio transmission, a continuous wave radio-frequency signal has its amplitude changed by an audio waveform before transportation. The audio waveform alters the amplitude of the carrier wave and defines the waveform envelope. In the frequency domain, amplitude modulation provides a signal with energy concentrated at the transmitter frequency and two adjacent sidebands. Each sideband is similar in bandwidth to the modulating signal and is a mirror reflection of the other.
Option (d) is correct.

Note:Single-sideband modulation utilizes bandpass filters to reduce one of the sidebands. Perhaps the carrier signal, which advances the ratio of message power to complete transmission power, decreases power handling specifications of line repeaters and enables better bandwidth use of the transmission medium.